https://registry.khronos.org/OpenGL-Refpages/gl4/html/glVertexAttribFormat.xhtml

says:

relativeoffset
The distance between elements within the buffer.

Section 10.3. in OpenGL 4.6 (Core Profile) - May 5, 2022 says:

relativeoffset is a byte offset of the first element relative to the start of the vertex
buffer binding this attribute fetches from.